Analog-to-digital conversion, which may include oversampling or shaping the quantization noise of a digital signal, is well-known and has a wide variety of applications, including digital audio, digital telephony, and digital instrumentation, to name only a few. Analog-to-digital conversion is discussed, for example, in "Oversampling Methods for A/D and D/A Conversion," by James C. Candy and Gabor C. Temes, appearing in the text Oversampling Delta-Sigma Data Converters: Theory, Design and Simulation, edited by James C. Candy and Gabor C. Temes, and published by IEEE Press (1992), "Oversampled, Linear Predictive and Noise-Shaping Coders of Order N&gt;1," by Stuart K. Tewksbury and Robert W. Hallock, and appearing in the aforementioned Candy and Temes text, "Optimal Nonrecursive Noise Shaping Filters for Oversampling Data Converters, Part 1: Theory" and "Optimal Nonrecursive Noise Shaping Filters for Oversampling Data Converters, Part 2: Applications" by Steven R. Norsworthy, appearing in IEEE Proc. ISCAS '93, Vol. 2, pp 1353-1360, May 1993, and "Idle Channel Tones and Dithering in Delta-Sigma Modulators," by Steven R. Norsworthy and David A. Rich, presented at the 95th Convention of the Audio Engineering Society, Oct. 7-10, 1993, all of the foregoing being herein incorporated by reference.
U.S. Pat. No. 5,144,308, entitled "Idle Channel Tone and Periodic Noise Suppression for Sigma-Delta Modulators Using High-Level Dither," by Steven R. Norsworthy, issued Sep. 1, 1992, assigned to the assignee of the present invention and herein incorporated by reference, discloses a technique for using a digitally generated dither signal to improve the performance of a sigma-delta modulator by reducing the amount of periodic noise and spurious tones generated in the converter output signal. A need exists to ensure that the dither signal generator is operating as intended and is having the desired effect on the output signal produced by the analog-to-digital converter; that is, a need exists to monitor or test the dither signal path.